The invention relates to a circuit arrangement for selecting in a data transmission system a diversity channel over which data is transmitted in the form of parity bits and information bits. Two or more diversity channels can be provided over which the data are transmitted in accordance with a space diversity process, time diversity process or frequency diversity process. At the transmitting end the items of data can be coded in the form of a convolutional code or a block code so that data faults are detected on the basis of received parity bits and information bits.
It is known to use diversity processes to improve the quality of the data transmission and to reduce the fault rate. The best transmission channel at one particular time can be found by measuring the receiving level of the signal transmitted over the individual channels and determining the highest level. Consequently, one switches through the channel which at a given time is transmitting the signal with the highest level. This known process does not always lead to the desired success, and in particular does not, when signals from an alien transmitter are transmitted at a high level across a channel. This is particularly disadvantageous when the alien transmitter is an interfering transmitter, so that it is the very channel which should under no circumstances be switched through which is given special preference. In such a case it can be advantageous to select the channels not in dependence upon the receiving level, but in dependence upon the received code words. When the parity words are dependent upon a large number of information bits, even the construction of one single channel will require a relatively large expenditure to be able to recognize any transmission faults. If not only one single channel, but a plurality of diversity channels must be checked, a proportionately greater cost must be expected.
An object of the invention is to provide a circuit arrangement of the type described hereinabove by means of which one of the diversity channels may be selected with a relatively low cost.